▎ 摘　　要

Motivated by the recent experimental observation [Abanin et al., Science 332, 328 (2011)] of nonlocality in magnetotransport near the Dirac point in six-terminal graphene Hall bars, for a wide range of temperatures and magnetic fields, we develop a nonequilibrium Green's function theory of this phenomenon. In the quantum-coherent regime and strong magnetic field, we find large Zeeman-splitting-driven spin Hall (SH) conductance in four-terminal bars, where the SH current is pure only at the Dirac point (DP). In six-terminal Hall bars, this leads to the nonlocal voltage at a remote location due to direct and inverse SH effect operating at the same time in different parts of the device. The "momentum-relaxing" dephasing reduces their values at the DP by two orders of magnitude while concurrently washing out any features away from the DP. Our theory is based on the Meir-Wingreen formula for spin-resolved charge currents with dephasing introduced via phenomenological many-body self-energies, which is then linearized for multiterminal geometries to extract currents and voltages. This provides a generalization of the multiprobe Landauer-Buttiker formula without employing traditional Buttiker voltage probes to introduce dephasing.